The Third Generation Partnership Project (3GPP) has lately initiated the LTE program to bring new technology, new network architecture, new configuration and new applications and services to the wireless cellular network in order to provide improved spectral efficiency and faster user experiences. At the same time, in order to continue to provide Multimedia broadcast Multicast services (MBMS) under the LTE network and technology, 3GPP has defined some new concepts and architectures for MBMS.
An objective of the Evolved Universal Mobile Telecommunication System (UMTS) project and UMTS Terrestrial Radio Access Network (UTRAN) project is to develop a packet optimized radio access network with high-data-rates, low-latency, and improved system capacity and coverage. In order to achieve this, improvements to the radio interface as well as the radio network architecture should be considered. For example, instead of using Code Division Multiple Access (CDMA), Orthogonal Frequency Division Multiple Access (OFDMA) and Frequency Division Multiple Access (FDMA) are being considered as air interface technologies to be used in the downlink and uplink transmissions, respectively. Another example is the application of packet switched services to an entire LTE network, resulting in all voice calls being made on a packet switched basis.
MBMS service is defined in the prior art. It is a counterpart of other multicast services operating in other spectrums, such as High Speed Digital Video Broadcasting (DVB-H). MBMS allows downlink data to be transmitted from a single source to multiple recipients in broadcast or multicast modes. The prior art also contains definitions of MBMS channels, scheduling, radio-bearers, procedures, and the like.
In the 3GPP LTE project, a new UTRAN and evolved core network have been introduced. Then new networks require changes to the current specifications for MBMS so that the new architecture can efficiently support MBMS services.
In a 3GPP LTE network, there are typically three types of cells; an MBMS dedicated cell, a mixed cell, and a unicast cell. The MBMS dedicated cell is dedicated to the downlink MBMS content transmission, and therefore there is no uplink access and function for any user equipment (UE). MBMS dedicated cells are usually deployed together, forming part of an MBMS synchronized transmission network (MBSFN) on the same frequency layer, (but different from the regular mixed/unicast LTE cells). The mixed cell has both the regular LTE cell's capability and also transmits downlink MBMS services and content over MBMS channels. The unicast cell is a regular LTE cell without MBMS service.
FIGS. 1(a)-1(c) show some examples of how the different cells may be deployed. In the prior art, when a WTRU switches to an MBMS dedicated cell from a unicast or mixed cell, the WTRU typically terminates the unicast service. The UTRAN can inform the WTRU of a new service request through paging.
It has been suggested that a single receiver WTRU should be able to receive MBMS services on a dedicated carrier and at the same time monitor paging for a possible incoming call. In general, there are two methods of paging a single receiver WTRU. One method is to transmit paging messages on an MBMS dedicated layer. Alternatively, the WTRU may transit or switch to a mixed or unicast cell to check for the incoming call paging.
Paging a WTRU that is receiving a signal on an MBMS dedicated layer has some problems. There may be problems with cell boundary update inefficiency and signaling overhead. The MBMS dedicated cell size typically is bigger than that of mixed cell, therefore a problem may result regarding how the WTRU that is operating on the MBMS dedicated layer detects that it has crossed the Tracking Area (TA) boundary. A WTRU cannot obtain any information regarding the change of TA while it operates in the MBMS dedicated layer.
Even if a WTRU can trigger a TA update (TAU), this will lead to an interruption of MBMS reception, since it can not be performed on the dedicated MBMS layer. Typically, a WTRU knows the scheduling pattern of the relevant MBMS services from the radio bearer (RB) configuration information and scheduling information. A WTRU typically returns to a camped unicast/mixed cell in the scheduled gap, and returns to the MBMS dedicated cell at the beginning of a scheduling data stream. During the interval, the WTRU may perform a non-MBMS procedure such as a TA or cell update. However, TAUs that are performed at too frequent a period may lead to large uplink signaling overhead.
A second problem may be paging inefficiency due to a large paging load. Typically, the size of a MBMS dedicated layer may be large and it may contain several unicast/mixed cell TAs along with a number of MBMS dedicated cells. If a paging channel is transmitted on a MBMS dedicated cell, it is possible that the paging request may be transmitted on the paging channels of all the MBMS dedicated cells, which may cause unnecessary system paging load. This may adversely reduce the effective data rate for the MBMS service.
Another problem may be delay while performing cell selection/reselection due to a WTRU's response to a paging signal, particularly when responding to an emergency service. This may cause a delayed paging response due to the cell selection/reselection process in the course of switching to the mixed/unicast cell after the reception of a paging signal in the MBMS dedicated cell. The impact may be severe when responding to an emergency call. In addition, signaling overhead might be a concern.
Assuming that a WTRU detects a number of neighboring cells, there is an estimated approximate 330 ms delay, on average, for the WTRU to perform cell selection or reselection and to get access to the mixed/unicast cell. This breaks down as 10 ms to perform measurements and 320 ms to read the relative broadcast channel (BCCH) information based on the system information broadcast (SIB) default schedule.
Another problem may be waste of resources when transmitting a paging message on both a MBMS dedicated cell and a mixed cell. It cannot be determined whether the paging is transmitted only on the MBMS dedicated layer or the paging is transmitted on the mixed cell and being duplicated on the MBMS dedicated layer. If the paging message is duplicated, paging messages will be transmitted on both the MBMS dedicated layer and the mixed cell. But the single receiver WTRU will be operating on the MBMS dedicated layer or the mixed cell only. Thus, the duplicated paging message may cause a waste of radio resources in one of these layers. It is thus desirable to provide more efficient paging as well as measurement schemes to aid in achieving significantly improved paging efficiency.
The current state of the LTE standards progress allows that an MBMS dedicated cell may also handle the regular WTRU idle mode paging. This is advantageous because a WTRU receiving MBMS service in the MBMS dedicated cell is able to monitor the possible incoming call paging without switching (inter-frequency switching) to a mixed cell or to a unicast cell, and therefore with no interruption to the MBMS service reception.
Therefore, in the LTE MBMS dedicated cell, there is a synchronization channel (SCH) for WTRU synchronization to the cell, a broadcast channel (BCH) for the WTRU to learn the system frame number and system information broadcast, the multicast channel (MCH) for the WTRU to receive MBMS related traffic, and the paging channel (PCH) for monitoring the incoming call paging.
There is a need to undertake the task to organize the WTRU's operations for MBMS service reception configuration, for paging monitoring and reception, for conveying to the WTRU the TA and the related cells association in order to allow the WTRU perform non-MBMS operations. It would be desirable to solve the dedicated cell paging arrangement problem and the tracking area update problem.